Every year 250 to 350 million dollars of chemical pesticides are used to control corn rootworm infections. Synthetic chemical pesticides are relatively expensive and, because of their toxicity to humans and wildlife, many have been banned from use. Many of the chemicals used for corn rootworm control are toxic to humans, wildlife and other nontarget species. Also, some have leaked into the ground water. As a result, much research has been concentrated in the area of biopesticides which have the advantage of being cheaper to produce and safer for the environment.
One commonly used biopesticide is the gram-positive bacterium Bacillus thuringiensis. Pesticidal B. thuringiensis strains are known to produce crystal proteins during sporulation which are specifically toxic to certain orders and species of insects and nematodes. (See, e.g., U.S. Pat. No. 4,999,192 and U.S. Pat. No. 5,208,017). Proteinaceous endotoxins produced by B. thuringiensis also act as insecticidal agents against corn rootworm and other beetles. For instance, delta-endotoxin is synthesized by the B. thuringiensis sporulation cell and, upon ingestion by susceptible larvae, is transformed into a biologically-active moiety that destroys the gut epithelium of the insect. (See, e.g., U.S. Pat. No. 5,427,786 to Payne et al.). Although B. thuringiensis endotoxins have been shown to be effective pesticides as purified crystals, washed cell pellets and expressed proteins, none of their supernatants have exhibited pesticidal activity.
Other B. thuringiensis thermostable proteins, termed beta-exotoxins, have also been shown to have pesticidal properties. Burgjeron and Biache (1979), Entomophaga: 11:279-284 report beta-exotoxins that are active against the Colorado potato beetle (Leptinotarsa decemlineata). In addition, known B. thuringiensis beta-exotoxins exhibit non-specific pesticidal activity; killing not only nematodes, but flies, armyworms and corn rootworms as well.
Stonard et al. (1994) ACS Symposium Series 551:25 report a water soluble secondary metabolite active against corn rootworm in the supernatant of a Bacillus cereus strain. Thus, there is a need for pesticidal B. thuringiensis strains which produce non-exotoxin active metabolites in their supernatant. There is also a need for a biocontrol agents which are specifically active against corn rootworm.